Liquid organopolysiloxane resins, a process for their preparation, low viscosity polydiorganosiloxane compositions containing liquid organopolysiloxane resins and their use

Claims

1. A low viscosity polydiorganosiloxane composition consisting essentially of

A) at least one liquid organopolysiloxane resin with the average composition

R.sup.1 is a C.sub.2 -C.sub.8 -alkenyl group,

R.sub.2 is an optionally substituted, linear or branched C.sub.1 -C.sub.8 -alkyl group or a mixture thereof,

a+b+c+d+e is about 1 to 6,

d+e is about 0 to 3,

the resin has a viscosity of 0.1 to 1000 Pas at 25.degree. C., and

the alkenyl content of the resin is in the range of 0.4 to 4 mmol/g,

B) at least one alkenyl-group-containing polydiorganosiloxane which is capable of cross-linking, of the formula

R.sub.3 and R.sup.4 each represent optionally substituted, linear or branched C.sub.1 -C.sub.8 -alkyl, C.sub.6 -C.sub.14 -aryl, or C.sub.2 -C.sub.8 -alkenyl,

x has a value which causes the viscosity of the resulting polymers (B) to be in the range of from 0.1 to 1000 Pas at 25.degree. C.,

C) at least one liquid polyorganohydrogensiloxane of the general formula

R.sup.6 is an optionally substituted, linear or branched C.sub.1 -C.sub.8 -alkyl group,

R.sup.5 has the same meaning as R.sup.6, or is hydrogen,

n and m each independently have a value which cause the viscosity of the resulting polymer (C) to be about 5 to 10000 mpas at 25.degree. C.,

or a polysiloxane which contains SiH groups, (SiO.sub.2)--groups, and (RSiO.sub.3/2)-- groups, wherein R represents an organo group,

D) at least one hydrosilylation catalyst from the group consisting of platinum group metals and their compounds,

E) optionally one or more fillers, and

F) optionally at least one further auxiliary agent.

2. A low viscosity polydiorganosiloxane composition according to claim 1, wherein

B) is blocked with dimethylvinylsiloxy groups and has a viscosity of 0.1 to 300 Pas at 25.degree. C.

4. A low viscosity polydiorganosiloxane composition according to claim 1, wherein in (C) the molar ratio of hydrogen to alkenyl groups is between 1:1 and 3:1.

5. A low viscosity polydiorganosiloxane composition according to claim 1, wherein the hydrosilylation catalyst is selected from the group consisting of a platinum(0) complex with a vinylsiloxane as ligand, hexachloroplatinic(IV) acid, and a complex thereof with an ethylenically unsaturated compound.

6. A low viscosity polydiorganosiloxane composition according to claim 5, wherein the platinum concentration in the hydrosilylation catalyst is 0.1 to 500 ppm of platinum, with respect to the total minute of components (A) to (F).

7. A low viscosity polydiorganosiloxane composition according claim 1, wherein a filler (E) is present and is optionally surface-modified with at least one member selected from the group consisting of a pyrogenic or precipitated finely divided silica with a BET surface area of 50 to 500 m.sup.2 /g, diatomaceous earth, finely divided quartz powder, amorphous silica, calcium carbonate, a metal oxide and carbon black.

8. A low viscosity polydiorganosiloxane composition according to claim 1, wherein at least one auxiliary agent (F) is present and is selected from the group consisting of 2-methyl-butyn(3)-ol-(2), ethynylocyclohexanol, tetramethylvinylcyclotetrasiloxane and 1,3-divinyl-1,1,3,3-tetramethyldivinyldisiloxane.

9. A low viscosity polydiorganosiloxane composition according to claim 1, containing

100 parts by wt. of A)

20 to 100 parts by wt. of B)

1 to 50 parts by wt. of C)

1 to 250 ppm of D), and

0 to 200 parts by wt. of E).

10. A low viscosity polydiorganosiloxane composition according to claim 3, wherein

(B) is a polydimethylsiloxane terminally blocked with dimethylvinylsiloxy groups with a viscosity of 0.1 to 300 Pas at 25.degree. C.,

(C) the molar ratio of hydrogen to alkenyl groups is between 1:1 and 3:1.

(D) the hydrosilylation catalyst is selected from the group consisting of a platinum(0) complex with a vinylsiloxane as ligand, hexachloroplatinic(IV) acid, and a complex thereof with an ethylenically unsaturated compound, and the platinum concentration in the hydrosilylation catalyst is 0.1 to 500 ppm of platinum, with respect to the total mixture of components (A) to (F),

(E) a filler is present and is optionally surface-modified with at least one member selected from the group consisting of a pyrogenic or precipitated finely divided silica with a BET surface area of 50 to 500 m.sup.2 /g, diatomaceous earth, finely divided quartz powder, amorphous silica, calcium carbonate, a metal oxide and carbon black, and

(F) at least one auxiliary agent is present and is selected from the group consisting of 2-methyl-butyn(3)-ol-(2), ethynylocyclohexanol, tetramethylvinylcyclotetrasiloxane and 1,3-divinyl- 1,1,3,3-tetramethyldivinyldisiloxane, the composition containing about,

100parts by wt. of (A)

20 to 100 parts by wt. of (B)

1 to 50 parts by wt. of (C)

1 to 250 ppm of (D), and

0 to 200 parts by wt. of (E).

11. An elastomer produced by vulcanizing a composition according to claim 1.

12. In the casting or embedding of an electronic or electrical components in the preparation of a mold or impression, or in the coating of a fabric by employing a liquid organopolysiloxane composition, the improvement which comprises employing as said composition a low viscosity polydiorganosiloxane composition according to claim 1.